Intravenous fluids are administered in almost all situations where invasive procedures are performed, where patients require repeated doses of injectable medications, where fluids or blood products are administered, and where a variety of tests are performed, as well as elsewhere. In order to regulate the volume of intravenous fluids that flow into a patient over a given period of time, thumb-wheel compression regulators are universally used. These thumb-wheel regulators (TWR) are manufactured in all intravenous fluid system tubing sold in the United States. Though the TWR is effective in controlling the rate of fluid infusion, it also acts as a restrictor when fluids need to be given rapidly. Though the TWR may be dialed “open” during this period, it may be cumbersome, especially when only an acute “bolus” of fluid is required, e.g., fluid used to flush an emergency drug into the patient.
Standard intravenous lines typically include: a) a proximal “spike and drip chamber” which is used to puncture a latex (or latex like) diaphragm on an intravenous fluid bag or bottle, or on a medication bottle, b) a length of PVC tubing, c) a TWR which is used to regulated the flow of fluid from the raised bag or bottle, and d) a distal connector which may be attached to a compatible intravenous catheter, or other components.
These systems allow the administration of fluids and drugs at a relative rate. The rate of fluid flow will depend on a) the height of the intravenous bag or bottle above the patient (e.g., gravity dependent), b) the set point of the TWR, c) the internal diameter of the intravenous catheter and d) resistance at the catheter-patient interface. Maximal flow will occur with the intravenous bag or bottle raised as high as the tubing and extension tubing will allow, a completely disengaged TWR, a large diameter intravenous catheter and a zero resistance catheter-patient interface.
Because of the limit of the length of tubing, the availability of large veins to accept large diameter catheters and non-zero resistance at the catheter-patient interface as flow through these systems may be slow. When flow is too rapid, the TWR is used to apply a restriction to flow.
When a drug must be delivered to the patient via the intravenous system, it is typically injected into an intravenous port or at the three-way stop cock. Once within the intravenous line, the rate of fluid flow of fluids from the intravenous bag or bottle will determine how rapidly the medication reaches the patient. This rate may not be rapid enough for the clinical situation. If the TWR is restricting flow, the caregiver may disengage the TWR, and then reengage it after he or she believes enough fluid flow has carried the medication into the patient. Often, and especially if flow in the system remains restricted after the disengagement of the TWR, a syringe is used at the injection port or three-way stop cock, to withdraw fluid (with negative pressure applied to the syringe) from the intravenous bag or bottle, which is then injected into the patient in order the “bolus” the medication to the patient (this is virtually impossible if the TWR is partially or fully engaged). Another way that flow may be increased is by squeezing the intravenous bag, creating a positive pressure force. If the TWR is not reengaged, the patient will continue to receive increased fluids, which, in some circumstances, may be detrimental.
In the neonate and infant population fluids are carefully regulated. Failure to reengage a TWR after a drug delivery can be devastating. Additionally, in this patient population, small boluses of fluid (e.g., 5 to 10 cc) may be used therapeutically (e.g., for hypotension). This requires constant disengage-reengagement of the TWR. Again, an error here may be devastating.